Throughout the past few decades, the semiconductor industry has developed many applications for wafer bonding. Through wafer bonding, semiconductor devices may be able to achieve advantageous features that they otherwise would not be able to achieve. For example, one of these applications is in making a structure with dissimilar materials. Wafers of different materials may be bonded together to form hetero-junctions, which may be useful in some semiconductor devices. Further, a thin film transferred by the bonding may have features useful for other devices, such as being stressed with a low density of defects.
Another application for wafer bonding is the bonding of a capping wafer to a device wafer, such as with micro-electro-mechanical systems (MEMS). In these applications, a capping wafer may hermetically seal a MEMS device to protect the device from exterior contamination and damage. Similarly, in other applications besides MEMS, a capping wafer may be used to provide protection and stability to an active device.
Typical processes for bonding a capping wafer to a device wafer have disadvantages. First, the capping wafer is usually thin, which typically requires thinning of the capping wafer. The thinning is generally performed after the capping wafer is bonded to the active wafer because a thin capping wafer is usually too thin to handle individually. This thinning, however, may introduce mechanical shock defects in a die formed by the bonding of the capping wafer and the active wafer. Further, individual dies are typically tested after bonding the capping wafer to the active wafer. This generally requires access to the individual dies, which typically cannot be achieved without dicing the capping wafer. Thus, wet dicing of the capping wafer is generally performed to allow access to individual dies. The wet dicing may cause further mechanical shock defects in resulting dies and may cause wet processing concerns, such as wet residues left on the dies.